Archive for April, 2015

So, this week I ran across a really cool paper published in 2013 in the journal Neuron by a team from Stanford University consisting of Josef Parvizi, Vinitha Rangarajan, William Shirer, Nikita Desai, and Michael Greicius. Actually, the first thing I ran across was this well-done article in the online magazine Quanta that featured the study when it came out. Then I went and looked at the published study.

It’s one of those studies you see sometimes that represent researchers’ taking advantage of a learning opportunity afforded by unusual circumstances. We’ve learned a great deal about the brain from these serendipitous windows of opportunity. In fact, for most of the history of brain science the biggest advances in our knowledge have come from unusual cases, such as victims of head injury, stroke, and so on. Some of the most interesting work of this kind has been done by scientists working with people whose brains are available to direct manipulation for reasons relating to medical circumstance. For example, we have Wilder Penfield’s seminal work in which he stimulated the exposed brains of conscious, aware epileptic patients and asked them about their subjective experiences, and Roger Sperry’s Nobel Prize-winning experiments with so-called “split-brain” patients whose corpora callosa (that’s the plural of corpus callosum – I looked it up!) had been surgically severed to prevent the spread of epileptic seizures from one hemisphere to the other.

The study by Parvizi et al. stands directly in this tradition. They were working with two epileptic patients and had the opportunity to implant electrically stimulating probes in the anterior midcingulate cortex of each. In case you’re wondering where that is, the following image shows the location of the stimulation site (marked with a yellow ‘1-2’) superimposed on each patient’s MRI scan:

This was part of a process whereby the researchers were assessing where in the patients’ brains their epileptic seizures were originating. With the patients conscious and interacting with them, they asked the patients to share any experiences that were generated when they turned on the current.

The results were quite striking. Both patients reported a similar experience, that was all the more remarkable because it had a complex, nuanced quality that wove together aspects of physiology, emotion, and intention. It would have been interesting enough had the stimulation resulted in a muscle twitch or seeing spots or something simple like that. What the authors described, though, was much more interesting. They entitled their paper “The Will to Persevere Induced by Electrical Stimulation of the Human Cingulate Gyrus”, and the “will to persevere” captures the patients’ experience rather well. Here’s the authors’ description of what happened:

Both patients reported autonomic symptoms including ‘‘shakiness’’ or ‘‘hot flashes’’ in the upper chest and neck region. Heart rate seemed to increase in both cases … Moreover, both patients recounted a sense of ‘‘challenge’’ or ‘‘worry’’ (also known as foreboding) but remained motivated and aware that they would overcome the challenge.

Both patients reported a sense that they were heading into a weighty and momentous challenge, and that they must bear up and persevere to get through it. It wasn’t fear, exactly, but a sense of challenge accompanied by a conviction that the patient would make it through. Here’s a snippet of video of one of the patients, published along with the journal article:

The authors noted that the stimulation site, in the anterior part of the midcingulate cortex, is a major node in what’s called the salience network, a set of mutually interconnected structures whose function seems to be to identify and register when something motivationally important happens in the environment, and to signal the need to engage other brain networks associated with effortful control (what neuroscientists call executive control) to deal with what’s happened. One of the authors on the paper, Michael Greicius, was one of the researchers who in 2007 first brought the salience network to the world’s attention and started mapping out its functions.

The authors of the current study confirmed that it was indeed the salience network that they had tweaked by identifying structures in each of the two patients’ brains whose activity levels (at rest, outside of the stimulation experiment) correlated with that of the stimulated site. The patients’ reported experiences align quite well with what the salience network is thought, on the basis of other, only slightly less cool research, to do.